BUY THAT CAR NOW!
What I would suggest, (and I'm sure others here will agree), make it a solid roof for the value... Or, look for a donor car with a fisher t-top roof (the larger t-tops) and as long as the roof and the glass are in good condition, do a roof swap. Then you'll have a Y-88 t-top car.
You could always contact Hitman and send him detailed photos and talk to him about a restoration, he restores TA's for a living and his work is absolutely beautiful.
http://www.taspecialties.com/resto/restore.htmThat's my 80' TA on the top left which is currently being brought back from the dead..
I will say this, you found a diamond in the ruff, hurry up and buy that car before the seller gets wind of the actual value of the car. Making it a hard top and restoring it would bring that car up into the $30k area. Doing a roof swap with a t-top car and a restoration could bring it up into the upper $30's and low to mid $40's..
The important thing to consider is that it's a genuine SE car, no matter what.
Scott